Exploring, drilling, and completing a hydrocarbon or other type of subterranean well is generally a complicated, time-consuming, and ultimately very expensive endeavor. As such, tremendous emphasis is commonly placed on well access in the hydrocarbon recovery industry. That is, access to a well at an oilfield for monitoring its condition and maintaining its proper health is of great importance. Such access to the well is often provided by way of coiled tubing, which is particularly well suited for being driven downhole to depths of several thousand feet by an injector located at the surface. The coiled tubing is generally of sufficient strength and durability to withstand such applications. For example, the coiled tubing may be of alloy steel, stainless steel, or other suitable metal-based materials.
Coiled tubing is deployed from a coiled tubing reel that can be manageably delivered to a well site. Despite being constructed of relatively durable materials, the coiled tubing plastically deforms while winding and unwinding from the reel, which affects the low cycle fatigue life of the coiled tubing. Repeated cycling (e.g., winding and unwinding) of the coiled tubing will eventually cause the coiled tubing to lose its structural integrity in terms of force bearing capacity or pressure bearing capacity. In extreme scenarios, the wall of the coiled tubing may fail at an over-fatigued location, thereby rendering the coiled tubing unsafe or wholly unusable. In order to avoid fatigue failure during operations, the coiled tubing is generally ‘retired’ once a predetermined fatigue life or limit has been reached.
To calculate when the predetermined fatigue life or limit has been reached, the coiled tubing reel may be equipped with a data storage system and processor configured to monitor historical cycling or bending of the coiled tubing during operations and comparing those determinations against a fatigue life model. A degree of accuracy may be provided whereby bending of each segment of the coiled tubing is tracked as it winds and unwinds from the reel and bends in one direction or another through the turns of the injector as it advances into or is retracted from a well. As such, from one operation to the next, the actual degree of cycling for any given segment may be historically tracked. Once segments of the coiled tubing begin to reach the limits established based on the fatigue life model, the process of retiring of the coiled tubing may ensue.
When coiled tubing is used in riser-less subsea operations, however, the coiled tubing is advanced into an oftentimes turbulent ocean environment. As a result, significant bending can be assumed by the coiled tubing as a result of subsea currents, ocean heaving, and other dynamic oceanic phenomena that may act on the coiled tubing. Such dynamic oceanic phenomena is difficult, if not impossible, to predict or model. As a result, unknown fatigue may be introduced into coiled tubing when deployed in riser-less subsea operations.